The invention relates to a high voltage rectifier, in particular for use as a bias voltage supply in vacuum processes such as PVD coating processes, comprising an input transformer and also subsequent rectification, smoothing and switching units and also an arrangement for switch control in dependence on occurring overcurrents. Furthermore, the invention is directed to an electronic control circuit which is particularly intended for use in connection with such a high voltage rectifier.
So far as PVD processes are concerned one can essentially distinguish between three process phases, namely the heating phase, the cleaning phase and the coating phase. During the heating phase heating and cleaning of the product is carried out by a ionised gas. The metal vaporizers are not switched on. The high voltage rectifier delivers the energy to the plasma. During the cleaning phase the metal vaporizers are switched on. Metal ions are generated by means of arcing and form a plasma of heavy ions. The substrate is kept during this at the highest maximum voltage value by the high voltage rectifier. In the coating phase the ions from the metal vaporizer are for example mixed with a gas and deposited onto the substrate. During this phase the high voltage rectifier which can generate a voltage of 1000 Vgs and higher delivers a lower voltage amounting to for example less than 400V.
With such coating processes the occurrence of arc discharges on the substrate, which represent short circuit-like loads for the high voltage rectifier are unavoidable and attempts must therefore be made to detect such arc discharges without delay in order to avoid the damaging effects which result from this and to remove the applied voltage from the substrate.
The object underlying the invention is thus to develop a high voltage rectifier of the initially named kind in such a way that arc discharges can be detected within a very short time, so that switching off can be made without delay following detection of an arc discharge and thus so that damaging effects on the substrate can be prevented.